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Abstract:

The present application claims a compact low cost topology solution of a
ballast for a discharge lamp that can provide both high power factor and
low total harmonic distortion with fewer components than prior art. The
topology provides the feature of a low crest factor and quick start that
increase both the lamp life and the number of starts for the product. By
using Bipolar Junction Transistor instead of Field Effect Transistor as
the main switches and also a lower value electrolytic, the cost and size
are considerably reduced.

Claims:

1. A circuit comprising:at least one high frequency full wave input bridge
diode;a resonant capacitor from an inverter circuit connected to one side
of the input bridge diode;a second capacitor from an inverter connected
to the other side of the input bridge diode in at least one of a direct
and an indirectly sequence; andat least one capacitor connected in
parallel with at least one input bridge diode.

2. The circuit of claim 1, wherein the at least one high frequency full
wave input bridge diodes are comprised of fast recovery diodes.

3. The circuit of claim 1, wherein the at least one high frequency full
wave input bridge diodes are comprised of at least one ultrafast recovery
diode.

4. The circuit of claim 1, wherein the first capacitor is a resonant
capacitor.

5. The circuit of claim 1, wherein the second capacitor is in series with
at least one Bipolar Junction Transistor, connected in series, in a half
bridge configuration.

6. The circuit of claim 1, wherein a four-diode bridge is located between
the input EMI filter and the at least one Bipolar Junction Transistor.

7. The circuit of claim 1, wherein an emitter terminal of one Bipolar
Junction Transistors is connected to a collector terminal of another
Bipolar Junction Transistor.

8. The circuit of claim 1, wherein each of the plurality of branch
circuits run from the input bridge, to a capacitor, to a lamp in series.

9. A circuit comprising:at least one high frequency full wave input bridge
diode;a resonant capacitor connected to the input bridge diode; anda
second capacitor, connected in at least one of direct and indirectly
sequence, from an inverter circuit connected to input bridge diode.

10. The circuit of claim 9, wherein the at least one high frequency full
wave input bridge diode is comprised of fast recovery diodes.

11. The circuit of claim 9, wherein the at least one high frequency full
wave input bridge diode is comprised of at least one ultrafast recovery
diode.

12. The circuit of claim 9, wherein the second capacitor connected in
series with at least one other capacitor.

13. The circuit of claim 9, wherein at least a third capacitor connected
in parallel with the input bridge diode.

14. The circuit of claim 9, wherein the high frequency of full wave input
bridge diode is greater than 20 Khz.

15. A base drive circuit with lamp voltage in direct sensing comprising:a
high frequency full wave input bridge diode;a base drive transformer
connected in series with a capacitor;a resonant capacitor connected to
the input bridge diode circuit and;a lamp connected to the base drive
transformer and second capacitor connected to the input bridge diode;

16. The circuit of claim 15, wherein the primary winding of the base drive
transformer is connected in series to the capacitor.

17. The circuit of claim 15, wherein the primary winding of the base drive
transformer connected in series to the capacitor is connected in parallel
with the lamp.

18. The circuit of claim 15, wherein the primary winding of the drive
transformer is inserted in series with a cathode of the lamp.

19. The circuit of claim 15, wherein the circuit contains a four-diode
bridge is located between an input EMI circuit and at least one of
Bipolar Junction Transistor.

20. The circuit of claim 15, wherein an emitter terminal of one Bipolar
Junction Transistor is connected to a collector terminal of another
Bipolar Junction Transistor.

21. The circuit of claim 15, wherein the plurality of Bipolar Junction
Transistors are connected in series in a half bridge configuration.

22. A base drive circuit with resonant input current sensing comprising:a
base driver derived from the insertion of a primary winding in series
with an input of a resonance tank circuit;two secondary circuits in
opposite phase connected to the bases of a plurality of Bipolar Junction
Transistors; anda plurality of input bridges, each connected in series to
a capacitor and to a lamp.

Description:

BACKGROUND OF THE DISCLOSURE

[0001]The present application is directed to electronic lighting systems,
and more particularly to an integrated bridge inverter circuit used in
connection with a discharge lamp.

[0002]Existing single-stage high-power factor electronic ballasts designed
for discharge lamps, such as integral compact fluorescent lamp
applications, have various drawbacks including an undesirably limited
zero-voltage switching range, a high unnecessary component stress during
operation and starting. Existing systems also have undesirably high crest
factors and high harmonics' content, which prevents products from
compliance with International Electro-technical Commission (e.g.,
IEC-61000-3-2) standards. Such lamps are also bulky and limit its usage
in space sensitive applications.

[0003]One existing electronic ballast which may be used for discharge
lamps is a self-oscillating high-power factor electronic ballast as
taught by Wong, U.S. Pat. No. 5,426,344. The Wong circuit, and other
ballasts in the art, use input bridge circuit portions and inverter
circuit portions which are distinct and separate from each other. The
Wong approach produces a crest factor of 2.0 or higher. The crest factor,
alternately referred to as peak-to-RMS (Root Mean Square) ratio is a
measurement of a waveform, calculated from the peak amplitude of the
waveform divided by the RMS value of the waveform. Crest factor is a
parameter that has direct impact on a lamp's life.

[0004]A disadvantage of the Wong approach is it produces a high
bus-voltage stresses, such as the voltage across a capacitor, which
requires use of high voltage-rated transistors. A further disadvantage of
the Wong approach is it requires a large EMI filter to moderate the
discontinuous nature of the input current existing prior to the input
diode bridge. The high-peak currents, which have higher high frequency
current content, need to be filtered out by the input EMI filter. A
further disadvantage of existing ballasts such as Wong et al., is a high
current stress on the switch transistors and resonant components.

[0005]Another related patent is Chen, U.S. Pat. No. 6,417,631 by the same
first inventor. This topology has eliminated many prior single stage
power factor correction (PFC) circuit drawbacks, however, it still uses a
larger number of components than a conventional compact fluorescent lamp
(CFL), and requires the use of more expensive FET switches.

[0007]An advantage resides in employing a circuit which uses fewer
components such as a capacitors, inductors, diodes, and uses less
expensive Bipolar Junction Transistors instead of field effect transistor
(FET), and thus also has a low cost to produce and to operate.

[0008]An advantage resides in the circuit having a combination of a high
power factor, a low total harmonic distortion, low crest factor and an
extended zero-voltage switching range.

[0009]A still further advantage resides in a low component stress on the
parts during the starting and operating of the light unit, resulting in
longer life of the ballast.

[0010]A still further advantage is that the design is extremely compact.

[0011]Still other features and benefits of the present disclosure will
become apparent from reading and understanding the following detailed
description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is an illustration of a schematic circuit diagram of an
embodiment of the present application.

[0013]FIG. 2 is an illustration of a schematic circuit diagram of an
embodiment of the present application.

[0014]FIG. 3 is a graphical presentation of a useful result of the
performance of an embodiment of the present application.

[0015]FIG. 4 is a graphical presentation of a useful result of the
performance of an embodiment of the present application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016]With reference to FIG. 1, a schematic circuit 100 of one embodiment
of the present application is presented. The legend 101 to the circuit
100 is also presented. The circuit 100 comprises an AC power source 110
located next to a fuse 112 that leads into a junction 113. One branch of
the junction leads to a filter and the other branch goes to an EMI
inductor 116 followed by a junction 121. The filter is comprised of a
capacitor 114 and a resistor 115 in series, and is followed by another
junction 117 that leads to the other terminal 111 of the power source and
a second branch which leads to another terminal 125. Both terminals 121
and 125 are on opposite ends of a capacitor 123. In an alternative
embodiment, it is possible for line 129 to be wired directly to point
121. In an alternative embodiment, it is possible for the line 127 to be
wired directly to point 125.

[0017]The inductor 116 side junction 121 connects to an outer loop line
127 that leads to a capacitor 197. This junction also connects to the
capacitor 123, to another capacitor 131, and to the middle of one side of
a four-diode bridge 130, between the diode 133 and the other diode 134.
Capacitor 131 and diode 133 both connect to inner loop 139, while diode
134 is connected to inner loop 149. In an alternative embodiment,
capacitor 131 may be moved to other points in the circuit such as but not
limited to be in parallel with diode 133, 134 or, diode 135 and 136 and
the like. In an alternative embodiment, there could be no capacitor or
more than one capacitor connected in parallel with diodes 133, 134, 135
and 136.

[0018]In an alternative embodiment, the diodes 133, 134, 135, 136 may be
collectively or individually removed and replaced by a pair of ultrafast
recovery diodes, wherein an ultrafast diode has similar specifications to
a regular diode, but has a 25 nanosecond or faster recovery. In still
further embodiment, the diodes 133, 134, 135, 136 can be integrated in
one package.

[0019]The non-inductor side junction 125 is connected to the capacitor 123
and an outer loop 129, which leads to a capacitor 199. In an alternative
embodiment, the lamp 193 is connected to junction 125 since the capacitor
199 and lamp 193 are connected in series. The junction 125 is also
connected to the middle of the other side of a four-diode bridge 130,
between the diode 135 and the other diode 136. Capacitor 131 and diode
135 are both connected to inner loop 139. Diode 136 is connected to inner
loop 149.

[0020]Both inner loop 139 and 149 connect to opposite ends of an energy
storage capacitor 137 and connect to a second common line 163. The
portion of the common line 163 closest to inner loop 139 contains two
resistors 141, 143 in series followed in series by a line 160 which lies
between the inner loop 139 and 149. A line 147 is connected between the
resistor 143 and the resistor 141. This line 147 connects to the central
line 160. The central line 160 contains a diode 145 between the resistor
141 and the line 147.

[0021]The central line 160 continues on and connects to a winding 154,
that is electrically coupled to an inductor 183, a resistor 155 and the
base terminal 151 of a transistor 150. The transistor 150 is comprised of
the B or base terminal 151, the C or collector terminal 152, and the E or
emitter terminal 153. The central line 160 also connects to another
resistor 156 and the E or emitter terminal 153 of the transistor 150. The
collector terminal 152 of this transistor 150 connects to the inner loop
139.

[0022]On the opposite side of the central line 160, connected to the same
line as the resistors 141, 143 a line connects a diac (diode for
alternating current) 165 to a capacitor 161. The other side of the
capacitor is connected to the inner loop 149. After the diac, a line
connects the diac diode to a junction, with one side of the junction
connected to a resistor 175 and a winding 176 also electrically coupled
to an inductor 183, connects to the inner line 149 and to circuit ground
177. The other side of the junction is connected to the base terminal 171
of a second transistor 170. The second transistor 170 is comprised of the
base terminal 171, the collector terminal 172, and the emitter terminal
173. The central line 160 also connects to another resistor 156 and the
emitter terminal 153 of the transistor 150. The collector terminal 172 of
the transistor 170 is connected to the central line 160 and the emitter
terminal 173 of the transistor 170 is connected to a resistor 174, which
is then connected to the inner loop 149. The inner loop 149 connects to a
capacitor 189 and to the central line 160 at a junction point 178.

[0023]The two inductors 183, 185 are connected in series and one side
connects to the junction point 178 and the other connects to the portion
187 of the outer loop bridge 196 that follow the capacitor 197. The
junction 187 is also connected to a lamp 190, by way of a line 191 to the
A terminal 192 of the lamp 193. The C terminal 194 of the lamp 193
assembly is connected by another line 195 to the portion of the inner
loop 198 that follows the capacitor 199. In an alternative embodiment,
the junction 187 is connected to the capacitor 199 and then to the lamp
193, because the capacitor 199 and lamp 193 are connected in series.

[0024]The four-diode bridge only conducts one at a time at the switching
frequencies of the inverter circuit when it is not on the peak changing.
The diodes 133 and 136 are alternately on and off during one half cycle,
while diodes 134 and 135 are on during the other half of the cycle of the
line cycle. The capacitor 197 also serves to provide the high frequency
feedback. Similarly the capacitor 199 also forces the diode to operate at
high frequencies due to feedback.

[0025]With the new topology, in the circuit arrangement, the Rk-a and Rk-b
circuit's base drivers 154 and 176 are derived from inserting the Rk-c
primary winding 183 in series with the input of the resonant tank
circuit. A tank circuit, also called a resonant circuit, provides the
energy to start and operate the lamp. The two secondary windings, Rk-a
154, and Rk-b 176, in opposite phase, are connected to the driver of the
two Bipolar Junction Transistor bases. The two Bipolar Junction
Transistors are connected in series and in half bridge configuration. In
this configuration, the primary winding not only senses the lamp's
current, but also the resonant current from capacitor 197. Since both the
branch of the circuit 197 and the lamp 199 are connected to the input
bridge, the line voltage modulates the effective capacitor values for the
capacitors 197 and 199. As the instantaneous line voltage varies, the
effective capacitor for capacitors 197 and 199 vary with it. Therefore,
the current to the input of the resonant tank changes. The base drivers
that sense from the input current to the resonant tank amplifies
differences over a half line cycle, as a result the crest factor of the
lamp is higher in the range of 1.8 to 2.0 which has negative impact on
lamp life. In addition, with large variation of the operating frequency
over the half line cycle, it is difficult to maintain zero voltage
switching of the Bipolar Junction Transistors and consequently the
temperature of the parts are high and life of the product is low.

[0026]The other drawback of this drive arrangement is that as a lamp
approaches end of life, the cathode may overheat and the cathode would
open. However, the inverter will continue to provide the energy to the
lamp and generate an even higher temperature around the cathode.

[0027]The high frequency operation of the input bridge circuit performs at
over 20,000 hertz. The high frequency circuit produces a low total
harmonic distortion, also called THD, and high power factor. Unlike a
conventional design, this design also will provide the advantage of
having a smaller integral lamp profile that will fit in most existing
fixtures. The existing high power factor ballasts include a separate
power factor correction stage, with additional components, that result in
larger complexity, higher price and larger size for the circuit.

[0028]This circuit design may also use a small value electrolytic that may
assure the continuous lamp current conduction, so the unwanted lamp
turn-off phenomena is avoided at each cycle that can significantly affect
the lamp life. The value of the electrolytic capacitor is sized just big
enough to accomplish this feature, but not too big which can hurt the
size and cost. The use of Bipolar Junction Transistor switches 150 with
the driver circuit, will give a low cost solution for the overall design.
This design provides better performance such as high PF and low THD than
do existing ballasts approaches, and contains fewer components which help
with the manufacturing process, compact size and lower cost.

[0029]The topology has the feature of using fewer components to achieve
premium features like high PF and low THD, all in a compact size. This
topology is the same size of the overall lamp like an regular, non-power
factor corrected, compact fluorescent lamp. In this disclosure two
versions of low cost Bipolar Junction Transistors based electronic
ballast circuits are presented. In both circuits, the mean operating
frequency is designed at about 100 Khz which is much higher than the
conventional circuit operated at about 40 Khz for the size consideration
of the magnetic and capacitors.

[0030]With reference to FIG. 2, schematic circuit diagram 200 of one
embodiment of the present application is presented. The diagram 200 shows
a new improved base drive arrangement for the new inverter circuit. The
device 200 comprises an AC power source 210 located next to a fuse 212
that leads into a junction 213. One branch of the junction leads to a
capacitor 215 the other followed by a junction 221. The capacitor 215 is
followed by another junction 217 that leads to the other terminal power
source 211 and a second branch which leads to another terminal 225. Both
terminals 221 and 225 are on opposite ends of a capacitor 223. In an
alternative embodiment, line 229 may be wired directly to point 221. In
an alternative embodiment, the line 227 may be wired directly to point
225.

[0031]The inductor 216 side junction 221 connects to an outer loop bridge
line 227 that leads to a capacitor 297. This junction also connects to
the capacitor 223, to another capacitor 231, and to the middle of one
side of a four-diode bridge 230, between the diode 233 and the other
diode 234. Capacitor 231 and diode 233 both connect to inner loop 239,
while diode 234 is connected to inner loop 249. In an alternative
embodiment, capacitor 231 may be moved to other points in the circuit
such as but not limited to be in parallel with diode 233, 234 or, diode
235 and 236 and, the like. In an alternative embodiment, there could be
no capacitor or more than one capacitor connected in parallel with diodes
133, 234, 235 and 236.

[0032]The non-inductor side junction 225 is connected to the capacitor 223
and an outer loop bridge 229, which leads to a capacitor 299. In an
alternative embodiment, the lamp 293 is connected to junction 225 since
the capacitor 299 and lamp 293 are connected in series. The junction 225
is also connected to the middle of the other side of a four-diode bridge
230, between the diode 235 and the other diode 236. Capacitor 231 and
diode 235 are both connected to inner loop 239. Diode 236 is connected to
inner loop 249. In an alternative embodiment, capacitor 231 may be moved
to other points in the circuit such as but not limited to other lines
227, 229, between diodes 233, 234 or between diodes 235, 236 and the
like. In a still further embodiment, the diodes 233, 234, 235, 236 may be
collectively or individually removed and replaced by at least one
ultrafast diode.

[0033]Both inner loops 239 and 249 connect to opposite ends of a capacitor
and connect to an central line 260 in between the inner loops 239, 249.
The portion of the common line 263 closest to inner loop 239 contains two
resistors 241, 243, in series followed in series by a line in between
inner loops 239 and 249. Line 247 is connected between the resistor 243
and the resistor 241. This line 247 connects to the central line 200. The
central line 260 contains a diode 245 between the resistor 241 and the
line 247.

[0034]The central line 260 connects to an winding 254, a resistor 255 and
the base terminal, 251 of a transistor 250. The transistor 250 is
comprised of the base terminal 251, the collector terminal 252, and the
emitter terminal 253. The central line 160 also connects to another
resistor 256 and the emitter terminal 253 of the transistor 250. The
central line 160 also connects to another resistor 256 and the emitter
junction 253 of the same transistor 250. The collector terminal 252 of
this transistor 250 connects to the inner loop 239.

[0035]On the opposite side of the central line 260, connected to the same
line as the resistors 241, 243 is connected a line that is connected to a
diac 265 and to a capacitor 261. The other side of the capacitor is
connected to the inner loop 249. After the diac, a line runs to a
junction, with one side of the junction connected to a resistor 275 and
winding 276, connects to the inner line 249 and to circuit ground 277.
The other side of the junction is connected to the base 271, base of a
second transistor 270. This transistor 270 is comprised of the B or base
terminal 271, the C or collector terminal 272, and the E or emitter
terminal 273. The central line 260 also connects to another resistor 256
and the collector terminal 273 of the transistor 270. The collector
terminal 272 of the transistor 270 is connected to the central line 260
and the emitter terminal of the transistor 273 is connected to a resistor
274, which is then connected to the inner loop 249. The inner loop 249
connects to a capacitor 289 and to the central line 260 at a junction
point 278.

[0036]The central line 260 is connected to an inductor 283 in series which
connect to the portion of the outer loop 296 that follow the capacitor
297. The central line 260 is also connected 287 to a lamp unit 290. The
lamp unit 290 comprised of a cathode 291 with a filament 292 with a
wattage rating 293 such as, but not limited to, 15 Watts. The lamp unit
290 also contains a second cathode 295 comprised of another filament 294.
Both filaments 292, 294 are connected together in series with a primary
winding 288 and a capacitor 285. The filaments of the second lamp 295 are
linked by a line 298 to the bridge 229. In an alternative embodiment, the
junction 287 is connected to the capacitor 299 and then to the lamp 293,
because the capacitor 299 and lamp 293 are connected in series.

[0037]The primary winding Rk-c of the base drive transformer 288 is
connected in series with the capacitor 285 and two cathode resistors 292
and 295 and then in parallel with the lamp. Since, lamp voltage changes
inversely to the lamp current, hence, the drive current which goes
through the primary drive transformer is also inverse to the lamp
current. The operating frequency over the half line cycle is also less
varied compared to the FIG. 1 circuit because of the negative feedback of
the drive characteristic. Therefore, the crest factor of the lamp in the
new circuit is substantially lower (1.5 to 1.65). The low crest factor
will extend the lamp life. This also provides a more effective means to
maintain the zero voltage switching for the Bipolar Junction Transistor,
increase the ballast efficiency and low temperature on the switching
devices.

[0038]Because the primary winding of drive transformer is now inserted in
series with the cathodes of the two lamps, in the event of one cathode
reaching and lamp life, the circuit will automatically stop operation
avoiding overheating of the lamp cathode.

[0039]With reference to FIG. 3, the waveform produced by the current
application 300 demonstrates the functionality of the circuit presented
in FIG. 1. The X-axis 310 represents time in five milli-second
increments, while the Y-axis 320 represents the variation in voltage
measured in volts and the variation in current measured in amps. The
waveforms for the connector to emitter voltage 330, the Bipolar Junction
Transistor's corrector current 340, the lamp's current 350 and the input
current 360 are each presented.

[0040]The legend of the graph 370 contains average values for the
respective waveforms. For the connector to emitter voltage 330 as
displayed in the graph legend, the value is 300 milliAmps per division
372. For the Bipolar Junction Transistor corrector current 340, the
average value is 100 Volts per division 374; for the lamp's current 350,
the scale is 300 milliAmps per division 376; and for the input current
360, the scale is 20 milliVolts per division 378. The lamp's current
waveform 350 of the lamp has a higher and longer sustained peak 380,
followed by a trough 385, followed by a smaller and less sustained
shorter peak 390, followed by a deeper trough 395. Here the peak 380 that
is longest in duration is also highest in peak.

[0041]With reference to FIG. 4, the waveform produced by the current
application 400 demonstrates the functionality of the circuit presented
in FIG. 1. The X-axis 410 represents time in 5 milli-Second increments,
while the Y-axis 420 represents the variation in voltage measured in
volts and the variation in current measured in amps. The waveforms for
the connector to emitter voltage 430, the Bipolar Junction Transistor's
corrector current 440, the lamp's current 450 and the input current 360
are each presented.

[0042]For the connector to emitter voltage 430 as per the legend on the
graph, the value is 300 milliAmps per division 472. For the Bipolar
Junction Transistor's corrector current 440, the scale is 100 Volts per
division 474; for the lamp's current 450, the scale is 300 milliAmps per
division 476; and for the input current 460, the scale is 20 millivolts
per division 478. The lamp's current waveform 450 has a small and
sustained peak 480, followed by a small trough 485, a higher but less
sustained peak 490, and a deep trough 495. Here the peak 480 that is the
longest in duration is also the lowest in peak.

[0043]A comparison of the lamp current waveform 350 on FIG. 3 with the
lamp current waveform 450 in FIG. 4 demonstrates the reduction in crest
factor. In FIG. 3, the sustained peak 380 is higher than the short peak
390. In FIG. 4, the sustained peak 480 is lower than the short peak 490.
Similarly, in FIG. 3 the deep trough 395 is deeper than the FIG. 4 deep
trough 495. The peak being of lower height and the troughs being
shallower demonstrates the reduction of the crest factor and also
demonstrates a useful, concrete and tangible result of the present
application.

[0044]The disclosure has been described with reference to the preferred
embodiments. Obviously, modifications and alterations will occur to
others upon reading and understanding the preceding detailed description.
It is intended that the invention be construed as including all such
modifications and alterations insofar as they come within the scope of
the appended claims or the equivalents thereof.